Introduction
When one mentions the words musical instrument, then what comes in any person’s mind is sound. Sound may be defined as the mechanical vibrations which are transmitted by an elastic medium or the part of a transmitted signal which is audible. Guitar is one of these instruments and it has been there for along time. We have various types of guitars having different sounds. The most common are the classical, or nylon string, and the folk which has steel string. Each produces a unique sound depending on the materials from which the strings are made and their bodies’ composition, as well as the air between them.
Construction
A guitar has six strings tied taught and are placed over a hollow large body to resonate the sounds. The strings have open notes of E2, A2, D3, G3, B3, and E4, with the corresponding frequencies of 82 Hz, 110 Hz, 147 Hz, 196 Hz, 247 Hz, 330 Hz respectively (Zachary, 1991). The frequencies listed are a representation of the root tone of each string. A guitar sounds as it does because of the overlay of various frequencies on individual string, or the overtones which are present. These overtones’ pattern and their strengths make a guitar produce different sound from other stringed instruments. The guitar also has a top plate which is usually made of spruce or a light, springy wood, about 2.5 mm thick. Inside the plate we have a series of braces which strengthen the plate and affect the vibrations of the top plate. The back plate is of much less importance musically for most frequencies. This is because it is normally held against the player’s body.
Working
When the strings are plucked, they produce mechanical vibrations which give sound that is transferred into the guitar’s body. The vibrations produced by a guitar are known as standing waves since the strings are fixed at both ends. These waves do satisfy the relationship that exists between wavelength and frequency that originates from definition of waves where v is the wave’s velocity, f is its frequency and lambda is the wavelength (Arthur, 1990). Due to these vibrations, internal resonance is setup in the air chamber which is made by the body and causes the face plate and back plate to vibrate. These vibrations produce compressions and rarefactions which are high pressure zones and low-pressure zones respectively. Our ear interprets compression waves in the air as sound. At any given point in the air, which is near the source of sound, the molecules move backward and forward resulting in the air pressure varying up and down by small amounts.
The principal role of the body is to transmit the bridge’s vibration into the vibration of the air which is around it. Thus, it needs a large surface area to enable it push reasonable amount of air backward and forward. The top plate is made in a manner to allow it to vibrate up and down comparatively easily. The air inside the body is very important for the low range on the instrument. It can vibrate like the air in a bottle when blown across the top. When you sing a note lying between F#2 and A2 (depending on the type of guitar) while you are placing your ear near the sound hole, you will hear the air in the body resonating. This is referred to as the Helmholtz resonance and is as result of the air at the sound hole oscillating, enabled by the springiness nature of the air found inside the body. The effect of this resonance may also be experienced by one playing the A string open and as it is sounds, a piece of cardboard is moved back and forth across the sound hole. It is observed that the resonance stops or shifts to a lower frequency. When you close up the hole, you will notice the loss of bass response in the sound given out. The air inside is coupled to the lowest resonance of the top plate effectively. As a unit they do give a strong resonance at approximately an octave higher than the main air resonance. To some extent the air also couples the movement of the top and back plates. For an electric guitar, pick-ups which employ the principle of magnetic induction in relaying sound are used. The pick-ups are made of small electromagnets which do allow electric current to flow through them. They are situated closely to the strings hence induce north and south poles on the strings. They do convert motion energy into electrical energy. Plucking a string makes it oscillate or move in a wave-line manner which does affect the surrounding o f the pick-up thus causing a change in magnetic field (Neville & Thomas, 1998). These fluctuations in the magnetic field are relayed through the wires which are connecting the pick-up to the output jack. This is then transmitted to the amplifier which then sends them to the speaker which converts from electrical energy to sound energy (George, 1990).
In conclusion, musical instruments do have different constructions and designs. However, they share one thing in common which is to produce organized sound pleasant to the ear. Most sources of sound produce different frequencies or several notes at the same time. For a good musical instrument, these notes are mixed at an organized pattern to produce music, and this is clearly experienced in a guitar which is my favorite instrument.
References
Arthur, H. B. (1990). Fundamentals of Musical Acoustics. New York: Dover Publications.
George, B. (1990). Making Stringed Instruments: A workshop Guide. New York: Sterling Publications.
Neville, H. F., Thomas, D. R. (1998). The Physics of Musical Instruments. New York: Springer Verlag.
Zachary, T. R. (1991). Making Early Stringed Instruments. New York: Bold Strummer.